1. Field of the Invention
The present invention relates to a piezoelectric micro electro-mechanical system (MEMS) switch, an array of piezoelectric MEMS switches, and a method of fabricating the piezoelectric MEMS switch, and more particularly, to a piezoelectric MEMS switch having an actuator in a cantilever form, an array of the switches, and a method of fabricating the piezoelectric MEMS switch.
2. Description of the Related Art
With the rapid development of information communication, small, light and high-performance information communication systems are highly in demand. Accordingly, the development of parts for the systems is urgent. In particular, one of such parts of the information communication system is a radio frequency (RF) switch that is used to control signals in the information communication system. Semiconductor switches, such as field effect transistors (FETs) or PIN diodes, have been widely used as RF switches. However, the semiconductor switches have problems of high power loss, signal distortion, non-linearity, high insertion loss, and low isolation.
In order to solve the problems associated with the semiconductor switches, much attention to a radio frequency micro electro mechanical system (RF MEMS) switch using a micro machining technique has recently been given.
An RF MEMS switch short-circuits or opens the RF transfer lines by a mechanical operation. This RF switch has less resistance loss than a semiconductor switch, uses low power, less signal distortion and high isolation. Thus, the RF MEMS switch can be applied to several fields such as digital controlled antennas, artificial satellite systems, mobile communication transmission and reception systems, and the like.
Such an RF MEMS switch may be actuated using an electrostatic-force actuating method, a magnetic-force actuating method, a thermal-deformation actuating method, and a pressure-based actuating method. The electrostatic-force actuating method has an advantage of low-power actuation, but the electrostatic-force actuating method has difficulties in actuating the switch at a low voltage of 3V or less, and thus a separate DC-DC converter is required. The use of the separate DC-DC converter causes power loss. The magnetic-force actuating method and thermal-deformation actuating method have a higher power loss than the electrostatic-force actuating method. Particularly, the thermal-deformation actuating method has a disadvantage of low response speed. Currently, a piezoelectric RF MEMS switch having less power consumption and higher response speed at a low driving voltage than the electrostatic-force, magnetic-force, and thermal-deformation methods is widely used.
Referring to FIG. 1, a conventional piezoelectric RF MEMS switch includes electrically separate RF transfer lines 10a and 10b, and a switching member 20 located under the RF transfer lines 10a and 10b for performing switching operations due to a piezoelectric phenomenon. An RF signal is applied to the RF transfer lines 10a and 10b. The long distance between the RF transfer lines 10a and 10b leads to excellent isolation, i.e., switching characteristics. The switching member 20 moves up similar to how an actuator having a piezoelectric layer (not shown) operates to electrically connect the separate RF transfer lines 10a and 10b. 
However, if the RF transfer lines 10a and 10b are spaced apart by a sufficient interval to obtain excellent isolation characteristics, i.e., switching characteristics of the MEMS switch, there is a drawback in that the shape of the switching member 20 deforms, i.e., when switching member moves up. That is, the switching member 20 needs to have a length as long as the distance between the RF transfer lines 10a and 10b and an actuator (not shown) having a piezoelectric layer for controlling the switching member 20 also needs to have a line width as long as the length of the switching member 20 in order to electrically connect RF transfer lines 10a and 10b which are sufficiently distanced apart. However, the increase in the line width of the actuator reduces a difference between the line width and the length of the actuator, and thus makes it difficult for the actuator to be strained longitudinally and a very high voltage is required by the actuator to move the switching member 20 to a desired height.
Furthermore, in order to lower an operation voltage in the conventional piezoelectric RF MEMS switch, a back surface of the semiconductor substrate on which the actuator is formed is etched so that the semiconductor substrate is penetrated. This increases processing time and costs. In addition, heavy stress is applied to the semiconductor substrate on which the actuator is formed.
After the piezoelectric RF MEMS switch is fabricated, the piezoelectric RF MEMS switch must be packaged in order to protect a moving structure therein. However, such a packaging process requires several processes including a wire bonding process and a molding process, furthermore complicating an entire process of fabricating the piezoelectric RF MEMS switch.